This invention relates to hydraulic controlled deflection rolls [such as are sold under the trademark "Swimming Roll" of Eduard Kuesters] in general and more particularly to an improved arrangement for such rolls which minimizes friction.
The rolls consist of a stationary core and a hollow roll or cylinder surrounding the stationary core with a spacing and rotatable thereabout. End seals are provided at the ends of the working width of the roll between the core and the hollow cylinder. Longitudinal seals are also provided along the core on both sides thereof. These seal the space between the core and the inside of the hollow cylinder so as to form a longitudinal chamber situated on the working side of the roll which is filled with the pressure liquid. Means are provided in the core for discharging leakage liquid from the space between the core and the hollow cylinder which remains between the core and the hollow cylinder on the side facing away from the working gap, i.e., from the area outside the longitudinal chamber.
Rolls of this type are known in principle from German Pat. Nos. 1,026,609 and 1,193,739, (See also U.S. Pat. No. 2,908,964), in which the longitudinal chamber extends over approximately one-half the circumference of the core, i.e., in which the sealing strips are arranged opposite each other at about half the height of the core. While in these designs the end seal is provided by a sealing plate arranged transversely to the axis, a roll is known from the Japanese Provisional Design Patent No. 5835/65, in which two parallel slots directed toward the roll gap are provided along the core. These slots are connected by circular slots at their ends. An endless sealing strip of corresponding shape is inserted into the entire slot, resting against the inner circumference of the hollow cylinder and enclosing the longitudinal chamber.
Since the working pressure is exerted in these rolls by the pressure liquid contained in the longitudinal chamber, it is uniform over the width of the web. Rolls of this type therefore are always used when accurate maintenance of uniform pressure over the width of the web is essential. This is the case particularly in the paper industry, where, with web widths of up to 10 m, uniform pressure cannot be exerted at all by other means.
For some time now, very high operating speeds in the range about 1500 m/min have been used in some applications. This can be the case in the area of paper manufacturing as well as paper converting and processing.
It has now been found that, with the required large increase of the running velocities, the power required for driving the rolls mentioned at the outset increases substantially. At higher speeds, the friction losses at the sealing strip become secondary to the friction of the hollow cylinder at the pressure liquid located between the core and the hollow cylinder. The viscous pressure liquid is contained in a relatively narrow space between the very rapidly revolving hollow cylinder and the stationary core and is carried along or held fast, respectively, at the boundary surfaces, so that a higher shear stress is developed. The larger the area of the circumference containing the pressure liquid, the higher become the losses due to liquid friction. The resistance component of the pressure liquid contained under pressure in the longitudinal chamber cannot be changed. However, a considerable resistance component is also supplied by the leakage liquid which escapes past the longitudinal seals into the space between the hollow cylinder and the core on the side facing away from the working gap. This liquid accumulates in the interspace, builds up in front of the longitudinal seal following in the direction of rotation of the hollow cylinder and, after some time, partially fills the interspace. An undesirable pressure buildup may, finally, even occur in the interspace.
In the arrangement described in German Offenlegungsschrift 24 61 914 it has been attempted to provide a remedy for this problem by making the longitudinal chamber in the circumferential direction particularly narrow. This, of course, also reduces the area available for exerting pressure. However, in the special embodiment dealt with in the German Offenlegungsschrift 24 61 914, the interest was only in rolls which must, at high speed, transmit only a small line pressure.